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Europe’s Large Hadron Collider tests the bounds of physics – and budgets

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The estimated price tag for the LHC is $5 billion to $10 billion.

How colliders work
At the high-energy frontier, physicists have been working with two groups of crash dummies: protons and their antimatter counterparts, antiprotons; and electrons and their mirror opposites, positrons. Each group has its own set of advantages and disadvantages, explains Harry Weerts, director of high-energy physics at Argonne National Laboratory in Argonne, Ill.

With the LHC, for instance, protons are the collision particles of choice. They carry an electrical charge (positive), which allows scientists to use magnets to focus the protons into tight beams and steer them around their circular racetrack. In the LHC’s case, the collider boasts more than 1,600 superconducting steering and focusing magnets. And protons have a respectable amount of mass, so scientists can whisk them around a bent path without the particles losing much energy.

But protons also have a drawback: They are made up of other particles – three quarks – that are bound to each other with yet more particles, called gluons. When protons collide, “it’s like colliding a bag of billiard balls with another bag of billiard balls,” Dr. Weerts says. The bags slam together, but the meaningful collision action is taking place among the billiard balls, not the sacks holding them. Indeed, he says, in reality, the LHC is really a quark collider.

By whatever name, the upshot is: The collisions are a mess. Scientists must sift through a lot of collision debris to spot the signatures of the particles they are trying to find. That requires long periods of operation to amass enough statistics on the collisions to convince themselves and their colleagues they have a genuine “eureka!” result.

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